1. Field of the Invention
This present invention relates to an electron source comprising a surface conduction typed electron emitting element and an image forming apparatus such as a display apparatus as an application of the electron source and, more particularly, to a method of manufacturing the same and a method of driving the same.
As conventional emitting elements, two types of elements, i.e., a thermonic cathode element and a cold cathode element are known. Of these elements, as a cold cathode element, a field emission type element (to be abbreviated as an FE type hereinafter), a metal-insulating layer-metal type emitting element (to be abbreviated as an MIM type hereinafter), a surface conduction type emitting element, and the like are known.
As an example of the FE type, for example, W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89, (1956), C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 52488 (1976), or the like is known.
As an example of the MIM type, for example, C. A. Mead, "Operation of tunnel-emission Devices", J. Appl. Phys., 32, 646 (1981), or the like is known.
As the surface condition type emitting element, for example, M. I. Elinson, Radio Eng. Electron Phys., 10, 1290(1965), or another example to be described below is known.
The surface conduction type emitting element utilizes a phenomenon in which electron emission takes place upon supplying a current to a small-area thin film formed on a substrate in a direction parallel to the film surface. As the surface conduction type emitting element, other than the above-mentioned element using an SnO.sub.2 thin film of Elinson, an element using an Au thin film G. Dittmer: "Thin Solid Films", 9, 317 (1972)!, an element using an In.sub.2 O.sub.3 /SnO.sub.2 thin film M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)!, an element using a carbon thin film Hisashi Araki, et al.: Vacuum, Vol. 26, No. 1, 22 (1983)!, and the like have been reported.
FIG. 39 is a plan view showing the above-mentioned element of M. Hartwell et al. as an example of the typical element structure of these surface conduction type emitting element. Referring to FIG. 39, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film consisting of a metal oxide formed by sputtering. The conductive thin film 3004 has an H-character planar shape, as shown in FIG. 39. When the conductive thin film 3004 is subjected to an energization treatment called energization forming (to be described later), an electron emitting portion 3005 is formed. An interval L in FIG. 39 is set to be 0.5 to 1 mm!, and W is set to be 0.1 mm!. Note that the electron emitting portion 3005 is illustrated in a rectangular pattern at the center of the conductive thin film 3004 for the sake of illustrative convenience, but it is merely an exemplary illustration one and does not faithfully express the position and shape of an actual electron emitting portion.
In the above-mentioned surface conduction type emitting elements such as the element of H. Hartwell et al., it is a common practice to perform an energization treatment called energization forming on the conductive thin film 3004 prior to electron emission, thereby forming the electron emitting portion 3005. More specifically, in the energization forming, the conductive thin film 3004 is energized by applying a constant DC voltage or a DC voltage which increases at a very slow rate (e.g., about 1 V/min) across the two terminals of the conductive thin film 3004 so as to locally destroy, deform, or denature the conductive thin film 3004, thereby forming the electron emitting portion 3005 in an electrically high-resistance state. Note that a fissure is formed in a portion of the locally destroyed, deformed, or denatured conductive thin film 3004. When a proper voltage is applied to the conductive thin film 3004 after the energization forming, electron emission occurs near the fissure.
The above-mentioned surface conduction type emitting element has an advantage of forming a large number of elements over a large area since its structure is simple and the manufacture is easy. For example, as disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 64-31332 by the present applicant, a method of driving an array of a large number of elements has been studied.
As for an application of the surface conduction type emitting element, image forming apparatuses such as an image display apparatus, an image recording apparatus, and the like, a charged beam source, and the like have been studied.
In particular, as an application to the image display apparatus, as disclosed in, e.g., U.S. Pat. No. 5,066,883 to or Japanese Patent Application Laid-Open (KOKAI) No. 2-257551 by the present applicant, an image display apparatus which uses a combination of a surface conduction type emitting element and a phosphor and the like which emit light upon irradiation of an electron beam has been studied. The image display apparatus which uses a combination of a surface conduction type emitting element and a phosphor and the like are expected to have better characteristics than those of conventional image display apparatuses adopting other systems. For example, as compared to a liquid crystal display apparatus which has become popular in recent years, this apparatus does not require any backlight since it is of self emission type, and has a wider viewing angle.